Computed Radiography (CR) is a process for capturing digital radiographic images. CR technology has been around since the early 1980s and has been widely accepted as a digital image acquisition process that produces images equivalent to conventional x-ray film-screen systems. For exposure, a storage phosphor plate (a photo-stimulable plate, or PSP) is placed in an x-ray cassette, instead of an X-ray film sheet. The storage phosphor plate fits inside a standard film cassette and is exposed to x-rays exactly like film.
Storage phosphor plates look like the intensifying screens found in conventional film-screen cassettes. However, instead of emitting light immediately when exposed to x-rays, they have the special property of storing the x-ray energy in a latent image. This latent image is “developed” in a CR reader, when the phosphor plate is scanned by a light beam, such as a laser beam. For example, the plate can be inserted into a CDCR 5020s, where it is scanned with a high power diode laser. The laser beam causes the storage phosphors to release UV light energy they have captured, in a photo-stimulable process. The CR reader extracts the information stored in the plate and this energy is converted into a digital image.
CR virtually eliminates the need for re-takes, eliminates lost images, simplifies the filing of images, and increases the capability for consultation made possible by electronic transmission of digital images. Storage phosphors also are unique because they respond to a very wide dynamic range of x-ray exposures. This latitude gives you flexibility in selecting x-ray technique without worrying about under or over exposure. Regardless of the exposure, the image can be displayed in an optimal fashion. As a consequence, retakes due to inappropriate exposures are drastically reduced.
After exposure and scanning, the phosphor plate is “erased” by exposing it to bright light. The residue of the previous latent image in the phosphors is removed, and the plate is ready to be exposed again. The life of a phosphor plate depends on how carefully it is handled. Physical damage to the plate will limit its useful life. There is nothing about the chemistry of the phosphors that degrades after repeated exposures. If properly cared for, a plate will produce thousands of images. In factory tests, a single plate has been scanned more than 10,000 times and was still in excellent condition. However, in conventional CR readers, the PSP is removed from the cassette before being inserted into the reader. In readers with rollers, the roller grabs the plate and can bend or rub the material, leading to reduced lifetime and image quality. Accordingly, two types of plates are currently in use—a substantially stiff plate which is difficult to bend, and a flexible plate which can be bent onto a cylinder for reading.
Traditional CR readers for mass production, as shown for example, in U.S. Pat. No. 4,778,995 to Kulpinksi et al. and U.S. Pat. No. 5,151,597 to Agano, include a flat support for the phosphor plate. The phosphor plate is held in the flat support while the optics in the CR reader scan the plate. However, this arrangement requires a complex system of optics in order to scan the phosphor plate, since the stimulating laser beam must be perpendicular to the plate when it is scanned. At present, this is accomplished by means of an Fθ lens, which is very expensive.
Accordingly, it has been suggested to utilize a curved support for the phosphor plate. For example, in U.S. Pat. No. 4,525,749 to Maeda et al. and U.S. Pat. No. 4,816,923 to Saotome, there are shown radiation image information readout devices having a sheet fixedly supported on the concave surface of a semi-cylindrical support during scanning by a light beam.
Cylindrical holders for photosensitive material are shown in U.S. Pat. No. 4,595,957 to Holthusen, and U.S. Pat. No. 6,207,968 and 6,291,831 to Koren, the latter providing scanning optics such that the light beam is at all times perpendicular to the medium at the point of impact of the beam with the medium. This system suffers from the disadvantage that the radius must be small, on the order of 90 mm, in order to achieve a compact device with a short laser path.
Accordingly, there is a long felt need for an inexpensive CR reading device providing a scanning beam perpendicular to the medium, and it would be very desirable to have such a device which doesn't damage photostimulable plates during the process of insertion and positioning.